To make the IFS:
Once you are in the world, on the dashboard, click on “My Airline” then “In Flight Service.” Then, click on “New Service Cabin” and fill out the IFS system.
Add the IFS to a route:
Click on “My Flights”, and go to the route you want to add the IFS to, and there will be a button right next to where you can change the price. You should be able to select your IFS from a drop down menu.